RE: [PATCH v3 2/4] rtc: pcf85363: Add support for NXP pcf85263 rtc

[Biju Das <biju.das@bp.renesas.com>]

Hi Geert,

Thanks for the feedback.

> Subject: Re: [PATCH v3 2/4] rtc: pcf85363: Add support for NXP pcf85263 rtc
>
> Hi Biju,
>
> On Thu, Dec 6, 2018 at 4:24 PM Biju Das <biju.das@bp.renesas.com> wrote:
> > > Subject: Re: [PATCH v3 2/4] rtc: pcf85363: Add support for NXP
> > > pcf85263 rtc CC nvmem maintainer
> > >
> > > On Thu, Dec 6, 2018 at 10:04 AM Biju Das <biju.das@bp.renesas.com>
> wrote:
> > > > Add support for NXP pcf85263 real-time clock. pcf85263 rtc is
> > > > compatible with pcf85363,except that pcf85363 has additional 64
> > > > bytes of
> > > RAM.
>
> > > > --- a/drivers/rtc/rtc-pcf85363.c
> > > > +++ b/drivers/rtc/rtc-pcf85363.c
> > > > @@ -120,6 +120,11 @@ struct pcf85363 {
> > > >         struct regmap           *regmap;
> > > >  };
> > > >
> > > > +struct pcf85x63_config {
> > > > +       struct regmap_config regmap;
> > > > +       unsigned int num_nvram;
> > > > +};
> > > > +
> > > >  static int pcf85363_rtc_read_time(struct device *dev, struct
> > > > rtc_time
> > > > *tm)  {
> > > >         struct pcf85363 *pcf85363 = dev_get_drvdata(dev); @@
> > > > -311,25
> > > > +316,68 @@ static int pcf85363_nvram_write(void *priv, unsigned
> > > > +int
> > > offset, void *val,
> > > >                                  val, bytes);  }
> > > >
> > > > -static const struct regmap_config regmap_config = {
> > > > -       .reg_bits = 8,
> > > > -       .val_bits = 8,
> > > > -       .max_register = 0x7f,
> > > > +static int pcf85x63_nvram_read(void *priv, unsigned int offset, void
> *val,
> > > > +                              size_t bytes)
> > >
> > > Given bytes should be 1, val should be a pointer to a single byte...
> > > What if bytes == 0?
> >
> > I doubt we get "bytes==0" because of the checks in "
> drivers/nvmem/core.c"
> > Function " bin_attr_nvmem_read/ bin_attr_nvmem_write".
>
> Depends. There are other functions calling nvmem_reg_{read,write}(), e.g.
> nvmem_device_{read,write}().

OK. In that case, I will return (-EINVAL)  for "bytes !=1"

> >
> > > > +{> +       struct pcf85363 *pcf85363 = priv;
> > > > +
> > > > +       return regmap_read(pcf85363->regmap, CTRL_RAMBYTE, val);
> > >
> > > However, regmap_read() has an unsigned int output parameter!
> > > So it's writing too many bytes, and only writing the actual data
> > > byte to the correct address on little-endian systems.
> > > Hence you need to use an intermediate variable to convert from
> > > unsigned int to byte.
> >
> > OK. Will use an intermediate integer variable.
> >
> > > > +}
> > > > +
> > > > +static int pcf85x63_nvram_write(void *priv, unsigned int offset, void
> *val,
> > > > +                               size_t bytes) {
> > > > +       struct pcf85363 *pcf85363 = priv;
> > > > +
> > > > +       return regmap_write(pcf85363->regmap, CTRL_RAMBYTE,
> > > > +                               *((unsigned int *)val));
> > >
> > > Likewise for writing.
> > >
> > > > +}
> > >
> > > BTW, while the nvmem_device_{read,write}() public API is documented,
> > > the
> > > nvmem_device.reg_{read,write}() driver API isn't.
> > > And the behavior might be confusing.
> > >
> > > E.g.
> > >  * Return: length of successful bytes read on success and negative
> > >  * error code on error.
> > >
> > > The public API seems to assume the driver API returns zero on
> > > success, and replaces the zero by the number of bytes requested.
> > > If the requested number of bytes is too large, a zero success would
> > > be converted to a value that's larger than the actual number of
> > > bytes transferred!
> > > However, the driver API can return a smaller (positive) number,
> > > which matches "standard" read/write() APIs.

Regards,
Biju


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